The inventions of the present application relate to a nickel-based single crystal alloy and also to a method of manufacturing the same. More particularly, they relate to a novel and highly strong nickel-based single crystal alloy having excellent strength at high temperature and anti-corrosive property at high temperature which is useful as a material to be used under high temperature and high stress such as turbine blades and turbine vanes for jet engines and gas turbines for industrial purposes.
Nickel-based single crystal alloys have been known as heat-resistant alloys used for high-temperature machinery and tools such as jet engines and gas turbines for industrial purposes.
For example, in order to promote the efficiency of gas turbine, it is the most effective method to raise the inlet gas temperature and, for such a purpose, it is essential to improve the high temperature strength of the materials used at high temperature and high stress. From such a viewpoint, there have been more and more improvements in the high temperature strenght of nickel-based superalloy year by year and, at present, with regard to the nickel-based single crystal superalloy, commercial alloys such as ReneN6 and CMSX10 which are called the third generation single crystal alloys have been developed and used.
Actually, however, those nickel-based single crystal superalloys of the third generation have problems. The first problem is that their solution heat treatment is not easy. In the nickel-based single crystal alloys of the third generation, the amount of chromium is reduced as much as possible and, in place of that, rhenium is added in large amount so that a decrease in corrosion resistance by a reduction of the amount of chromium is compensated by rhenium whereby good corrosion resistance at high temperature is maintained and a high strength at the medium temperature of up to 1,000xc2x0 C. is achieved.
However, the heat treatment of those nickel-based single crystal alloys of the third generation is becoming to higher temperature and becoming complicated as well. For example, in the case of CMSX-10, about ten steps of solution treatments for 45 hours in total at 1,360xc2x0 C. at the highest are necessary.
Accordingly, there has been a practical demand for new technical means whereby strength at high temperature can be improved without deteriorating the corrosion resistance at high temperature and, in addition, the solution heat treatment is easy.
In addition to the above problem, there is another problem that, as a material for high temperature for actual use, a harmful phase is formed within a short period during the use at the temperature of as high as not lower than 1,000xc2x0 C. Then, the third problem is that, due to said harmful phase, the strength lowers to the level of same as or even lower than that of the second generation single crystal superalloys at conditions of high temperature for long time.
Under such circumstances, the inventions of the present application are to solve the above-mentioned problems in the nickel-based single crystal alloys of the third generation and to offer novel nickel-based single crystal alloy where the solution heat treatment is easy and strength at high temperature and corrosion resistance at high temperature are excellent and also to offer a method of manufacturing the same.
In order to solve the above-mentioned problems, the first invention of the present application offers a nickel-based single crystal alloy, characterized in that, the composition consists of 7-15 of Co, 0.1-4 of Cr, 1-4 of Mo, 4-7 of W, 5.5-6.5 of Al, 5-7 of Ta, 4-5.5 of Re, 0-0.5 each of Hf and V, and 0-2 each of Ti and Nb in terms of % by weight and residual part substantially consists of Ni where said alloy may contain unavoidable impurities.
The present application further offers a nickel-based single crystal alloy according to the above-mentioned first invention wherein said alloy contains 10-14 of Co, 2-3 of Cr, 1.5-2.5 of Mo, 5-6.5 of W, 5.7-6.3 of Al, 5.5-6.5 of Ta, 4.5-5 of Re and 0.01-0.3 of Hf in terms of % by weight.
The present application furthermore offers a method of manufacturing a nickel-based single crystal alloy as mentioned in the above first or second invention, characterized in that, a solution heat treatment is conducted at the temperature range of 1,310-1,350xc2x0 C. and a aging heat treatment is conducted at the temperature range of 850-1,200xc2x0 C.
The prevent application still furthermore offers a method of manufacturing the nickel-based single crystal alloy according to the above-mentioned method wherein the solution heat treatment is conducted within ten hours and the aging heat treatment is conducted within thirty hours; a method of manufacturing the nickel-based single crystal alloy wherein each of the solution heat treatment and the aging heat treatment is conducted in a single step or by means of temperature changes in two to four steps; and a method of manufacturing the nickel-based single crystal alloy wherein a preliminary thermal treatment at from 1,290xc2x0 C. to lower than 1,310xc2x0 C. for two hours or shorter is conducted prior to the solution heat treatment.